(A) Schematic illustration of a FLP/FRT-mediated tkv allele switch. mCherry-tagged Tkv expression was specifically induced in the wing pouch via FLP/FRT-mediated recombination that eliminates tkv-GFP from the locus. White and grey boxes represent tkv coding and 3’UTR sequences, respectively. (B–G) tkvGFP>>mCherry heterozygous animal before and after allele switch. (B, C, E, F) GFP (green) and mCherry (red) represent endogenous Tkv expression in the developing wing disc. BMP/DPP activity was detected by anti-p-Mad staining (grey). (D, G) Both Tkv-GFP and Tkv-mCherry expressing animals developed normal adult wings. Longitudinal veins L2-L5 are indicated. (H–J) Wing pouch-specific allele switch of the constitutively active form of Tkv, TkvQ199D. TkvQ199D-mCherry (red) expression led to ectopic p-Mad activation (grey, H, I), resulting in wing malformation (J). Scale bars: 50 μm for (B), and 0.5 mm for (D). Anterior is oriented to the left in all wing disc figures and to the top in adult wing images.